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来源：Xjng
www.cnblogs.com/Xjng/p/5120853.html
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一.c，ctypes和python的数据类型的对应关系
ctypes type ctype Python type
c_char char 1-character string
c_wchar wchar_t 1-character unicode string
c_byte char int/long
c_ubyte unsigned char int/long
c_short short int/long
c_ushort unsigned short int/long
c_int int int/long
c_uint unsigned int int/long
c_long long int/long
c_ulong unsigned long int/long
c_longlong __int64 or long long int/long
c_ulonglong unsigned __int64 or unsigned long long int/long
c_float float float
c_double double float
c_char_p char * (NUL terminated) string or None
c_wchar_p wchar_t * (NUL terminated) unicode or None
c_void_p void * int/long or None
2.操作int
>>> from ctypes import *
>>> c=c_int(34)
>>> c
c_int(34)
>>> c.value
34
>>>
c.value=343
>>> c.value
343
3.操作字符串
>>> p=create_string_buffer(10)
>>> p.raw
'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
>>> p.value='fefefe'
>>> p.raw
'fefefe\x00\x00\x00\x00'
>>> p
.value='fefeeeeeeeeeeeeeeeeeeeeeee' #字符串太长，报错
Traceback (most recent call last):
File "", line 1, in <module>
ValueError: string too long
4.操作指针
>>> i
=c_int(999)
>>> pi=pointer(i)
>>> pi
<__main__.LP_c_int object at 0x7f7be1983b00>
>>> pi.value
Traceback (most recent call last):
File
"", line 1, in <module>
AttributeError: 'LP_c_int' object has no attribute 'value'
>>> pi.contents
c_int(999)
>>> pi.contents=
c_long(34343)
>>> pi.contents
c_int(34343)
通过pointer获取一个值的指针
通过contents获取一个指针的值
5.c的结构体
#定义一个c的structure，包含两个成员变量x和y
>>> class POINT(Structure):
... _fields_=[('x',c_int),('y',c_int)]
...
>>> point=POINT(2,4)
>>> point
<__main__.POINT object at 0x7f7be1983b90>
>>> point.x,point.y
(2, 4
)
>>> porint=POINT(y=2)
>>> porint
<__main__.POINT object at 0x7f7be1983cb0>
>>> point=POINT(y=2)
>>> point.x
,point.y
(0, 2)
定义一个类型为POINT的数组
>>> POINT_ARRAY=POINT*3
>>> pa=POINT_ARRAY(POINT(2,3),POINT(2,4),POINT(
2,5))
>>> for i in pa:print pa.y
...
Traceback (most recent call last):
File "", line 1
, in <module>
AttributeError: 'POINT_Array_3' object has no attribute 'y'
>>> for i in pa:print i.y
...
3
4
5
6.访问so文件
1.创建一个c文件
#include
int hello_world(){
printf("Hello World\n");
return 0;
}
int main(){
hello_world();
return 0;
}
2.编译成动态链接库
gcc hello_world.c -fPIC -shared -o hello_world.so
3.python中调用库中的函数
from ctypes import cdll
c_lib=cdll.
LoadLibrary('./hello_world.so')
c_lib.hello_world()
二.测试c的性能和python的差别
sum.c
int sum(int num){
long sum=0;
int i =0;
for( i=
1;i<=num;i++){
sum=sum+i;
};
return sum;
}
int main(){
printf("%d",sum(
10));
return 0;
}
1. 直接用c来执行，通linux 的time命令来记录执行的用时
sum.c：
#include
int sum(int num){
long sum=0;
int i =0;
for(
i=1;i<=num;i++){
sum=sum+i;
};
return sum;
}
int main(){
int i ;
for (i=0;i<1000000;i++){
sum(100);
}
return 0;
}
测试结果的例子：
real 1.16
user 1.13
sys 0.01
2.通过Python调用so文件和python的测试结果
sum_test.py:
def sum_python(num):
s
= 0
for i in xrange(1,num+1):
s += i
return s
from ctypes import cdll
c_lib = cdll.LoadLibrary('./sum.so')
def sum_c(num):
return c_lib.sum(num)
def test(num):
import timeit
t1 = timeit.Timer('c_lib.sum(%d)' % num, 'from __main__ import c_lib')
t2 = timeit.Timer('sum_python(%d)' % num, 'from __main__ import sum_python')
print 'c', t1.timeit(number=1000000)
print 'python', t2.
timeit(number=1000000)
if __name__ == '__main__':
test(100)
测试结果的例子
c 1.02756714821
python 7.90672802925
3.测试erlang的测试结果
刚刚学了erlang，那就一起测试一下erlang的运算性能
sum.erl:
-module(sum).
-export([sum/2,
sum_test/2]).
sum(0,Sum) ->
Sum;
sum(Num,Sum) ->
sum(Num-1,Sum+Num).
sum_test(Num
,0) ->
0;
sum_test(Num,Times) ->
sum(Num,0),
sum_test(Num,Times-1).
调用：
timer:tc(sum,sum_test,[100,1000000]).
测试结果的例子：
{2418486,0}
4.测试结果
用上面的测试方法，进行10次测试，去除最大值和最小值，再计算平均值，得出：
单位：秒
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